Chances are close to zero.

Whatever game they’re working on they hired David Wise to do the music. He’s most famous for Donkey Kong Country and Diddy Kong Racing. I doubt they would get him to be the composer for a Smash Bros game.

Something Donkey Kong related is almost certain. I wouldn’t put Diddy Kong Racing  as beyond questionable either given that Nintendo clearly had that sort of game in mind for them to develop at some point (since they've had them training design and development of Mario Kart tracks).

What we do know is they hired David Wise (DKC/Diddy Kong Racing) and that they prominently place Mario Kart racing on their About page (which, admittedly is out of date, but you'd think they would remove that if it were no longer relevant). They're also working with Monster, who specializes in racing games (Excitebots, Nascar, Test Drive, Excite Truck, Excite Bike).

As far as the dev time argument. Keep in mind, Retro is really really sluggish when it comes to dev times.

I suspect Diddy Kong Racing given the evidence, although this could be wrong, they also worked with David Wise and Monster Games on Tropical Freeze.

Its gonna be another Donkey Kong Games. Its going to be tons of laughs and giggles.

i have no expectations so if they reveal DK i won't be disappointed

Considering timing (assuming they will announce it this year) it may be an online multiplayer game. But definetly they're not developing Smash Bros, HAL and Bamco are already proficient at that.

It's actually StarTropics

What makes you think that? They have no experience with online engineering and haven't hired any online specialized engineers.

Hopefully not. I've never been able to get into Smash.

I don't really think Smash is the secret Retro title. I honestly think we'll just get Smash 4 with all of the WiiU and 3DS content, plus the DLC characters and costumes. The game is absolutely filled to the brim with content, it would be a shame starting again from scratch. Let Retro make a new IP.

I don't know who they have hired over these year. I'm just going by the fact that most of the AAA online gaming industry is based in the US. They have an higher chance of attracting skilled online engeneers and designers than in japan. Also since Nintendo announced their online platform is coming later this year they'll want a killer app to sell it, because that's how they usually operate.

 Good points, I was hoping you’d have some evidence though as it would REALLY help my Diddy Kong Racing theory =P

If Retro + David Wise + Racing game experience + Monster Games Collaboration + Online functionality came together, that would point more to DKR than DK3D Platformer.